Troubleshooting a Plumbing Problem the Electronics Way

Often water flow is used to explain basic electronics in the form of analogies. After learning the hard way, an engineer attempts to explain basic water flow in terms of electronics.

Often water flow is used to explain basic electronics in the form of analogies. In this blog, after learning the hard way, I will attempt to explain basic water flow in terms of electronics.

It started one morning with a wet carpet just outside the laundry room and the water heater. The water was warm, and the puddle started at the base of the water heater which had no drip pan. We assumed that the water heater had sprung a leak, which is a typical mode of their behavior.

While I had done some copper pipe soldering many years ago, I felt that installing a new water heater was probably beyond my basic plumbing skills, so we had the heater replaced by professionals. They showed up at 9:00 a.m. and had the job done by noon, as my wife reported while I was at work. My draining the tank ahead of time might have helped.

But then about 3:00 p.m. my wife called back to report that the carpet was still getting soaked even after sucking up the water with the carpet cleaner. And the puddle was hot, so this was not a residual puddle from water still hidden under the wall. Uh-oh -- sounds like a leaky pipe inside the wall.

The heater hot water outlet entered the laundry room wall about six feet above floor level, and I assumed it went straight down from there. I had two choices: I could drain and move the new water heater and cut through the wall behind it, or I could investigate from the other side of the wall (which happened to be the rear inside of a kitchen cabinet). Due to laziness, I chose the latter to start with.

After measuring from the laundry room side of the wall I used a three-inch hole saw to cut out the rear of the kitchen cabinet and through the drywall halfway from floor level, and luckily got centered over the pipe the first time. It was wet. Then I drilled another 3-inch diameter circular cutout two feet higher -- the pipe was dry.

Bingo! I now knew approximately the location of the leak -- about two feet above the concrete floor. It was very fortunate that the leak was not below the concrete slab! After cutting out a larger section of wall and peeling back all the thermal insulation materials, I saw what is in the picture below. So I set up a small funnel and short drainage hose into a large cooking pot to collect the leakage while pondering (no pun intended) what to do:

The sliced-open tin can was planned as a heat shield for my brand-new propane torch to solder the pinhole closed. Yeah, right.

I shut off the cold water intake valve to the water heater, opened all the household hot water faucets, and waited for the above stream to subside. And waited... and waited... and waited.

After many fruitless hours I finally concluded that maybe the shower and kitchen faucets that combined the hot and cold feeds into a single outlet might be allowing the still-pressurized cold feed to leak over into the hot system. Something like this with a "leaky" lower diode, consider the incoming cold water pressure as akin to a positive DC voltage:

My hypothesis was later confirmed by a friendly, long-experienced, retired plumber at the local home improvement center. He referred to it as "cross-feed," similar to what we know as "cross-talk." Ask these guys, they have a lot of good tips for novices. And it did work -- shutting off the outdoor curbside main cold water feed stopped the flow from the pin hole a few minutes later.

But now the situation was a lot more serious -- lack of hot water is an annoyance (cold showers, etc.), but NO water is a magnitude more of a problem. We take for granted how easy it is to flush a toilet, and it's not always mellow yellow. (Note to renovators -- always make sure your new shower/bath/kitchen faucets have two individual hot/cold controls.)

No big deal, I thought, just solder the pinhole closed once the water stops leaking out. Well, we fluxed and tried over and over again. The solder simply would not flow. Having done a lot of electronics soldering, I recognized that even with the torch going full blast the pipe was not getting hot enough. And judging from the steam hissing from the pinhole, there was still standing water in the pipe at the pinhole level, and being at the lowest elevation it had nowhere else to go.

I tried snaking some 1/4-inch icemaker tubing as a siphon down the hot water pipe that by now had been disconnected from the heater (thankfully the new heater had been installed with flexible pipe with threaded attachments instead of the original soldered piping) and sucking on it to remove the standing water (gross!). It seemed to work -- for a few minutes. Then the water level rose back up to the pinhole, I could still see a small trickle leaking out again. In electronic terms, here is what was happening:

Both the hot and cold systems had water stored in the higher-elevation pipes, represented by the capacitors. Discharging at the pinhole let the remaining stored water drain back to the level of the pinhole through the "leaky-diode faucets" and slowly escape. This would take forever to drain out through the tiny pinhole, or to be sucked out through the mouth-operated siphon, which I wasn't looking forward to doing again.

The only way to speed up the discharge process was to bite the bullet and remove the water heater again, cut into the drywall behind it, and with a brand-new, mini-hacksaw made for this purpose cut three inches of the bad section out of the pipe so that a six-inch "repair coupling" could be soldered in. This allowed most of the standing water to discharge quickly, but only down to the level of the lower cut-off pipe. Now the situation looked like this:

The capacitor voltage (water level) cannot discharge below the forward bias voltage of the silicon diode. A residual charge will remain since the electrons have nowhere to go. The standing water in the lower pipe also had nowhere to go, and the pipes still could not be soldered.

To discharge a capacitor, it must have a current path. A negative current source can discharge it. In this water case, a wet/dry shop vac coupled to the cut-off pipe through a duct-taped "impedance matching network" to seal the air flow for maximum suction transfer, along with opened water faucets throughout the house, did the job nicely. With no more standing water I was finally able to solder the new section of pipe in.

Thank goodness for duct tape and shop-vacs!

In retrospect, had I thought of using the wet/dry vac first, I could have simply attached it to the hot water pipe removed from the top of the water heater and applied the suction there. Would have saved me a lot of work, and I would have been able to solder the pinhole through the rear wall of the kitchen cabinet instead of moving the heater and cutting into the drywall.

Next time I will know better. Maybe this experience will help another neophyte with a similar plumbing emergency.

— Glen Chenier is an old-timer who grew up with vacuum tubes and therefore has been amazed and fascinated by the many advances in the electronics industry since.

@PRZEM Do you run the risk of becoming the family "go-to" guy/girl (or help desk) when you learn a special skill? Or is that potentially a good thing? I had a brother-in-law who would come with my sister to visit and take care of all of the handyman type things while he was supposedly "on vacation." Tightening loose latches, repairing our screen door, and other kinds of marvelous things.

That jogged my memory, while working on refrigeration systems , we had this epoxy stick http://www.laco.com/repair-sealants/heat-seal-stik/ , it looked like a big green crayon, you cleaned up around the leak, then heated the pipe (150C??), and just rubbed the "crayon" on the leak, I used it once when there was no access for soldering and it's pretty strong as the refrig system could get to > 200Psi.

Another product I found in my old refrig kit is "RedEpoxy" , this is a two part epoxy you mix up seperately, then apply it to a warmed section of pipe, then apply heat till it goes gold, takes a minute, and it's good for 300psi. http://www.highsidechem.com/redepoxy.html

Both of the above can be obtained from a HVAC shop and are specifically designed for high pressure leak fixes. You also have a range of kneadable epoxies similar to marine-tex like this one http://www.laco.com/repair-sealants/epoxy-stik-/ personally I've had mixed results with kneaded epoxies, they tend to be porous.

Also, to make an analogy between the eductor and a transistor, you'd have to go to the (relatively uncommon) common base configuration. In this configuration, the "bias" voltage would be the water pressure being fed by the water supply to one of the legs of the Y connection (aka transistor's collector). The other leg of the Y connection would be the base. The bottom of the Y, which spits our the supply water plus whatever the pump sucks up, is the emitter.

So what happens is that as water pressure is applied to the "collector" of this pump, some "base" current will flow (into the transistor, current from ground through the base), and the sum of collector and base current flows out the emitter. But notice, no voltage gain here, just as there isn't any pressure gain in an eductor.

A regular water faucet is probably a more typical analogy to a transistor, say in emitter follower (common collector) configuration. Water pressure is applied at the "collector," and then a relatively small effort at the faucet's tap (base) will cause a large change in "emitter" water flow. The pressure of the water out of the faucet won't exceed the pressure of the water feeding the faucet, just as in an emitter follower amp, but you'll get large gains between effort applied at the tap and the amount of water flow and pressure out of the faucet.

Eductors can be super efficient pumps, e.g. for de-flooding, if you feed them, say, with typical firemain pressures.

Marine-Tex is an epoxy putty that has myriad uses around boats. A guy I used to work for that owned a 30' Egg Harbor said he'd know someone that used it to fix a crack in an intake manifold. The engine heat helped it to set quicker!

Yep you pretty much have it in your last paragraph. The nozzles I use are orange, and bought from a $1 shop in Buffalo (on one of my visits to the US).

(I've not heard of "hydraulic monitor" before but now we have google! I do recall seeing them used on a History channel show, some sort of gold? mining operation)

You also need two lengths of 1/2" hose , about 3' long, with the click-lock fittings at each end. (I use PVC tubing instead as it's more flexible)

So you basically split the water supply into two using the Y piece with the valves, sometimes you need to turn off one or both of nozzle and suction; and have a 3' length of hose for each of the nozzle and ejector.

Ok "adobe" just seems to be dried dirt? domestic water pressure should cut that OK (without resorting to a pressure cleaner) (we have "silcrete" in the western parts of Australia , it's like asphalt!)

You need to make a deep corner in your excavation, this is the sump, the suction unit shoud be contrived to be 1/2" above the bottom, so it doesnt suck onto the bottom of the sump, a small piece of wire netting (1/2" holes or smaller) (like used in aviaries) can be used to form a basket around the bottom , this also catches big chunks that might cause blockages. You would normally leave the suction unit in the one place.

If it's a flat pond or has many low spots you might need to move the suction unit around a bit. I've usually emptied ponds down to ~ 1-2" with the pond pump first. The wire mesh basket prevents damage to any fish you might accidentally try to suck up.

Avoid hydrostatic issues by discharging the water a long way from the pond and waiting several days after heavy rain.

The venturi is fine sucking air, it generally works best sucking half air and half muddy water . You will spend half your time cutting and the other half chasing the mud into the sump.

A secondary issue is what to do with the pile of mud and muddy water at the exit hose , if diverted to a shallow tub , you can then recover about half of the volume of dirt. Or maybe a large piece of shade cloth? or weed mat?

I am having trouble visualizing how all this connects together. We have a pond which could probably use a vacuum.

I also use something like a hydraulic monitor for cutting under the sidewalk. (a plastic nozzle with a taper on it.)

I need to fix some sprinklers, but with the drought here in Northern CA, the adobe soil is like brick. The monitor would cut it, exept all the water pools in the adobe, and has to be pumped out.

I know about venturis from the rocket group I am president of. These things work on air or other fluid. (I have a 19th century textbook on the subject.)

What I can not visualize is how the venturi connects to the monitor and can move the silty mud that backs up in the hole. Where does the Y valve fit in. Does this connect to the water supply with one leg to the venturi and the other to the monitor? If the venturi port is sucking in air, what keeps it from being clogged?

if you search on ebay for " pond suction -cup " you will find some pictures of e.g. a "mud sucker" and a "pond mini-vac"

You can make one yourself by starting with say a 1" plastic tee, and screwing in a reducing bush with a hose adapter and a hose tail (for a nozzle) . I used to make them myself, (then discovered I could buy better ones for less than the $30/hr to make them! )

Continuing the electronic analogy theme of the original blog...

An ejector is very much like a transistor , you push a current of fluid into the "base" , this causes it to suck up stuff through the "collector" and eject the sum of both flows out the "emitter" (a PNP might be easier to visualise) . Homebuilt ones might have a HFe of 1 to 5 , store bought units maybe 10 to 50

I mow my own lawn with a ride-on mower ,because it takes me 30 min to get it in and out of shed (even if the gardener drives it) , but I leave all the edge trimming , pruning and weeding to him.

With plumbing sometimes its half and half, its silly to pay someone $100/ hr to dig holes , so at least you can dig holes/ lift pavers etc so when the plumber arrives his billable time is short. Sometimes after doing all the prep, you find you can fix it yourself. Irrigation systems are a good example of this.

(BTW I'm in Australia) Recently I needed an ultrasound , the nearest diagnostic imaging company, about 10kms away, wanted ~$400 and couldn't do it for a month. But a private hospital some 50km's away could do it for free the same day.

Given that I already had to drive somewhere, the 80km extra round trip distance amounted to 90 mins of my time in order to save $400, So that's $266/hr , way more than $30/hr